Objectives Dutch primary out-of-hours care is provided by general practice cooperatives (GPCs). Although most GPCs use the same standardised triage system, differences between GPCs exist in the urgency assigned to patients’ health problems. This cross-sectional study aims to provide insight into factors associated with the variation in assigned urgency between GPCs. Design and methods Data were derived from routine electronic health records of 895 253 patients who attended 17 GPCs in 2012. Patients’ gender, age, travel distance to the GPC, and the use of a computer-based decision support system for triage were investigated as possibly affecting assigned urgency. Multilevel linear regression analyses were executed for the 3 most frequently presented health problems (cystitis/other urinary infection, laceration/cut and fever). Results Variation in urgency levels between GPCs was significant for the selected health problems (p=0.00). Assigned urgency was mainly related to patient gender and age. It was not associated with the use of a computer-based decision support system, or with travel distance to the GPC. Most variation in urgency (93.4–96.7%) could be ascribed to variation in patient characteristics. Conclusions There is significant variation in urgency levels between GPCs, even for the same health problem. This variation is mainly associated with differences in characteristics of individuals contacting the GPCs, rather than with variables such as patients’ travel distance or the use of a computer-based decision support system. Since patient characteristics are likely to affect patients’ clinical need, our results are an indication of the adequate functioning of the triage system.